Automatic grinding mill controls responsive to mill conditions to control the grinding process are known in the art. Exemplary of general mill controls are U.S. Pat. No. 4,026,479 issued to R. G. Bradburn et al., May 31, 1977; U.S. Pat. No. 4,210,290 issued to R. E. P. Andersson et al., July 1, 1980; and U.S. Pat. No. 4,212,429 issued to J. P. Cuvelier et al., July 15, 1980.
The control of a mill to conform to a desired reference condition is taught in U.S. Pat. No. 2,766,941 issued to D. Weston, Oct. 16, 1956. Calculations based on conditions found in the mill complex for controlling the flow of materials therein are known for example in U.S. Pat. No. 4,281,800 issued to M. D. Flavel, Aug. 4, 1981 and U.S. Pat. No. 3,783,252 issued to R. E. J. Putman on Jan. 1, 1974, which take into account a variable grindability of the input materials. In U.S. Pat. No. 3,860,804 issued to R. E. Rutman, Jan. 14, 1975 is shown a computer to control the grinding process in accordance with a control algorithm to improve the flow rate of the material being ground. British Patent Specification No. 854782, published Nov. 23, 1960 derives a control signal as a function of the dynamic mill increasing or decreasing power variation to keep power in the mill at a maximum.
The beforementioned parent application for the first time introduced computer controlled automatic monitoring systems taking into account the effect of chemical additives used for improvement of grinding efficiency in ball mill type grinding system complexes. The effect of chemicals on the efficiency and cost of grinding is significant and thus it becomes necessary for any automatic grinding control systems to have the capacity for control of the flow of chemicals as well as basic raw materials to be ground. All the hereinbefore cited prior art systems have the common deficiency that they control only with one variable control of the primary material flow path, and the use of chemical additive grinding aids can completely mask and overcome the effect of that type of automatic control.
Accordingly, it becomes necessary to resolve the problem of automatically controlling the flow of materials in a grinding system complex for meeting predetermined objectives such as maximum throughput volume or maximum grinding efficiency in the presence of various kinds and quantities of chemical additives. The additional criterion of controlling for the most efficient use of the optimum flow of chemical additives, is not addressed in the prior art, and presents a serious economic problem in view of the relatively high cost of the chemical additives over the usual materials being ground.
Also other control problems encountered in the grinding process are not addressed in the prior art, particularly relating to the control of the grinding process in the presence of chemical additives, such as the following:
(a) the ability to derive meaningful true change of flow signal from the grinding process that will vary significantly enough and not be masked by a high level of throughput volume,
(b) the ability to control interactions between different flow rates in different parts of the grinding system complex and between different flow rates for different grinding process material constituents,
(c) significantly long times are taken to correct large deviations from flow rates such as occurred at startup or upon changes in grinding materials, etc., and
(d) the lack of system operating data or appropriate readily available operational data permitting diagnosis of the system operations by computer analysis to determine operating characteristics and feasible modes of system improvement.
It is therefore an objective of the present invention to resolve the foregoing problems. Other features, objectives and advantages of the invention will be found throughout the following description, drawing and claims.